High pressure centrifugal fuel pumps for use in an aerospace environment are required to be light in weight and extremely rugged in their construction. Moreover, every additional ounce of weight that can be removed from such a fuel pump is an ounce of weight that does not have to be carried aloft over the life of the aircraft. Current aircraft remain airworthy for twenty years or more. The fuel cost per ounce of aircraft weight just to maintain the aircraft aloft for more than twenty years is significant and measurable in dollars and cents.
The use of unitary diffuser rings in centrifugal compressors as in the K. H. Wieland U.S. Pat. No. 4,302,150, where the medium being pumped is a gas, is common.
High pressure liquid pumps of the centrifugal type that include diffuser rings in conjunction with a pump impeller and high pressure fluid delivery volute are typical as shown by the Cygnor et al U.S. Pat. No. 4,417,851, and the Schaefer U.S. Pat. No 4,714,405, both of which are assigned to the same assignee as the subject invention.
In high pressure fuel pumps, the diffuser rings are typically clamped between pump support structures and held in a unitary assembly by means of bolts that pass through the diffuser ring and secure the ring to the support structures. Because of the extremely high fluid pressures in and about the diffuser ring assembly, pump fastening bolts are frequently inserted through openings in the diffuser ring at points between adjacent diffuser throats.
It has been discovered that the tremendous loads experienced by the pump fastening bolts find their origin in the fact that while the diffuser ring is clamped between support structures, surfaces of the diffuser ring adjacent the support structures are wetted by the fluid being pumped. These wetted faces of the diffuser ring are exposed to a range of fluid pressures from the fluid that exits at pump impeller and the pressure at an exit end of a diffuser throat of the diffuser ring. It will be appreciated that when these just described fluid pressures are present over a diffuser ring surface, a force equal to the product of the area of the diffuser ring face times the fluid pressures over the diffuser ring surface will be present. The just described force must be accommodated by the pump fastening bolts. None of the U.S. patents cited hereinbefore appear to recognize this just described force nor do they suggest any way to reduce such a force, as the instant invention does, in a manner to be describe hereinafter, thereby allowing for the reduction in size and number of the pump fastening bolts.